Numerous geodetic surveying appliances have been known for surveying one or particularly more targets since ancient times. In this context, the range and direction or angle from a measuring appliance to the target to be surveyed are recorded and also, in particular, the absolute position of the measuring appliance together with any existent reference points are captured as spatial standard data.
Generally known examples of such geodetic surveying appliances are a theodolite, a tachymeter and a total station, which is also called an electronic tachymeter or computer tachymeter. A geodetic measuring apparatus from the prior art is described in the published document EP 1 686 350, for example. Such appliances have electrosensory angle and distance measuring functions that allow a direction and distance to a selected target to be determined. In this case, the angle and distance variables are ascertained in the internal reference system of the appliance and may also need to be linked to an external reference system for absolute position determination.
In many geodetic applications, points are surveyed by placing specially designed target objects at said points. These usually consist of a plumb rod having a targetable module, e.g. with a reflector for defining the measurement path or the measurement point. These target objects are targeted by means of a surveying appliance, a direction and a distance to the objects are determined and hence a position of the objects is derived.
In a similar manner to this point surveying, it is possible to mark targets that already have known coordinates or points whose position has been defined in advance of a marking process. In contrast to point surveying, in this case the position and the coordinates of the points to be marked are known and need to be marked. Such a process usually likewise involves the use of a plumb rod or surveying rod that is carried by a user and is positioned on a target. To this end, the user can approach the target position of the target on the basis of position information generated by the surveying appliance, the surveying rod being automatically targeted by the surveying appliance by a second person or by automation associated with the surveying appliance. Once the target has been reached, the user can mark the point.
Modern surveying appliances such as a total station have microprocessors for digital further processing and storage of captured measurement data. The appliances are usually manufactured in a compact and integrated design, with coaxial distance and angle measuring elements and also computation, control and memory units usually being integrated in one appliance. Depending on the expansion level of the total station, means for motorizing the target optical system, for reflectorless path measurement, for automatic target searching and tracking and for remote control of the overall appliance are integrated.
Furthermore, total stations known from the prior art have a radio data interface for setting up a radio link to external peripheral components, such as to a data capture appliance, which may particularly be in the form of a hand-held data logger, remote control unit, field computer, notebook, small computer or PDA. The data interface can be used to output measurement data captured and stored by the total station for external further processing, to read externally captured measurement data for storage and/or further processing into the total station, to input and output remote control signals for remotely controlling the total station or a further external component, particularly in mobile field use, and to load control software into the total station.
To sight or target the target to be surveyed, geodetic surveying appliances of the type in question have, by way of example, a telescopic sight, such as an optical telescope, as a sighting device. The telescopic sight is generally able to rotate about a vertical axis and about a horizontal tilt axis relative to a base of the measuring appliance, so that the telescope can be oriented to the point to be surveyed by means of swiveling and tilting. Modern appliances can have, in addition to the optical viewing channel, a camera, integrated into the telescopic sight and having a coaxial or parallel orientation, for example, for capturing an image, wherein the captured image can be presented particularly as a live image on the display of the indicator control unit and/or on a display of the peripheral appliance used for remote control—such as the data logger or remote control unit. In this case, the optical system of the sighting device may have a manual focus—for example an adjusting screw for altering the position of a focusing optical system—, may have an autofocus, with the focus position being altered by servomotors, for example, or may have fixed focusing in conjunction with a wide angle lens. Automatic focusing devices for telescopic sights on geodetic appliances are known from DE 197 107 22, DE 199 267 06 or DE 199 495 80, for example.
EP 1 734 336 discloses a surveying system having a target unit that has a reflector and also an optical receiver and transmitter. In this case, it is proposed that the optical transmitter of the target unit be used for supporting the automatic target searching process, inter alia. Thus, following reception of the search or measurement radiation, the target object can transmit its own identification, such as the reflector number or the reflector type, back to the surveying station using the transmitter of the target unit. The surveying station can therefore identify the sought target object and configure itself in optimum fashion for the target object.
A common feature of the aforementioned surveying systems from the prior art is that, possibly also using a camera, the target unit or a surveying rod provided with the target unit is targeted or observed by a stationary position determination unit, such as a total station. However, no automated guidance of an operator, using the image data recorded by the stationary position determination unit, to a provided target for the purpose of marking the latter is disclosed, which means that the marking process is relatively laborious for an operator and has considerable associated time involvement if precise marking of the target needs to be ensured.
For a solution to this problem, U.S. Pat. No. 7,222,021 and the corresponding EP 1 293 755 propose a surveying system, referred to as a user guidance system in this patent specification, having a stationary base station corresponding to a stationary position determination unit, which is equipped with depiction means, such as a camera, and a mobile station having the function of a mobile target unit, which is equipped with display means, such as a display for presenting a current position of the user on the basis of stored landscape images or data and current images, seen from the stationary measuring unit. Furthermore, it is disclosed how a user can be guided to the target by means of correlation between the position data for the mobile station that are currently measured from the stationary measuring station and stored data from the envisaged position of the target by marking on the display of the target unit. This can be supported by the use of a camera image, with the user being able to be guided by a direction and distance display, for example, by means of an arrow on the display.
Although this system described in U.S. Pat. No. 7,222,021 and in the corresponding EP 1 293 755 can be used to speed up the process of marking a target, the disclosure does not reveal any possibilities for improving the accuracy of the marking of the target. Real images are captured only by means of the stationary total station, which is remote from the mobile station, while the mobile station, such as a plumb rod with reflector, is guided using only synthetic, calculated presentations from a bird's eye perspective on a mobile display.
Accordingly, one disadvantage is that the user with a plumb rod cannot be guided without restriction on the basis of a real presentation of the terrain. In particular, this is the case when there is a relatively great distance between the total station and the target and a simultaneous relatively short range between the plumb rod and the target. Guidance by means of an arrow presented in the image is difficult or impossible in this case—on account of a constant camera perspective or because, when targeting the reflector on the plumb rod, the camera is likewise oriented thereto and hence the terrain is captured from a perspective that does not or does not fully permit simultaneous presentation of the arrow from the plumb rod position to the target position in the image. In addition, the display of the arrow in the display can—depending on the guidance direction—conceal a portion of the camera image such that obstacles in the immediate surroundings of the user, for example, or further targets to be surveyed are concealed.